I have a jvc kd x255bt head unit. It has only 2 sets of preamp outputs front and switchable rear/subwoofer. I also have a monoblock amp with only a LPF. I also have 2 2-way coaxial speakers for the front of the van and 2 2-way coaxial speakers for the rear of my van which will not be powered by a external amp. So I was wondering what speaker/preout setting should I set it to in the head unit; to Rear/Subw or Subw/Subw if my front and rear speakers arent powered by an external amp? Also my head unit has HPF/LPF crossovers in it. Can I set the LPF on the amp and leave the LPF in the head unit alone and use the HPF in the head unit since my mono amp has no HPF?